sdk/1.0/docs/man/restrictions.xml

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<refentry>
	<refentryinfo>
		<keywordset><keyword>restrictions</keyword></keywordset>
	</refentryinfo>
    <refmeta>
        <refentrytitle>restrictions</refentrytitle>
		<refmiscinfo>
            <copyright>
                <year>2007-2009</year>
                <holder>The Khronos Group Inc. 
 Permission is hereby granted, free of charge, to any person obtaining a
copy of this software and/or associated documentation files (the
"Materials"), to deal in the Materials without restriction, including
without limitation the rights to use, copy, modify, merge, publish,
distribute, sublicense, and/or sell copies of the Materials, and to
permit persons to whom the Materials are furnished to do so, subject to
the condition that this copyright notice and permission notice shall be included
in all copies or substantial portions of the Materials.</holder>
            </copyright>
        </refmiscinfo>
        <manvolnum>2</manvolnum>
    </refmeta>
	
<!-- ================================ SYNOPSIS -->	

  <refnamediv id="restrictionsref">
<refname>Restrictions</refname> 
           <refpurpose> </refpurpose> 
</refnamediv> 
 
    <refsect1 id="restrictions"><title></title>
		<itemizedlist mark="disc">
		
		<listitem>
			<para>The use of pointers is somewhat restricted. The following rules apply:</para>
			<itemizedlist mark="opencircle">
				<listitem>
				<para>Arguments to <citerefentry href="functionQualifiers"><refentrytitle>__kernel</refentrytitle></citerefentry> functions declared in a program that are pointers must be declared with the __global, __constant or __local qualifier.</para>
				</listitem>
				<listitem>
<para>A pointer declared with the <citerefentry href="constant"><refentrytitle>__constant</refentrytitle></citerefentry>, <citerefentry href="local"><refentrytitle>__local</refentrytitle></citerefentry>, or <citerefentry href="global"><refentrytitle>__global</refentrytitle></citerefentry> qualifier can
only be assigned to a pointer declared with the __constant, __local, or __global qualifier respectively.</para>
				</listitem>
				<listitem>
<para>Pointers to functions are not allowed.</para>
				</listitem>
				<listitem>
<para>Arguments to <citerefentry href="functionQualifiers"><refentrytitle>__kernel</refentrytitle></citerefentry> functions in a program cannot be declared as a pointer to a pointer(s). Variables inside a function or arguments to non __kernel functions in a
program can be declared as a pointer to a pointer(s).</para>
				</listitem>
			</itemizedlist>
		</listitem>
		<listitem>
		<para>Variables that are declared to be of type <citerefentry href="otherDataTypes"><refentrytitle>image2d_t</refentrytitle></citerefentry> or <citerefentry href="otherDataTypes"><refentrytitle>image3d_t</refentrytitle></citerefentry> refer to image
memory objects. These can only be specified as arguments to a function. Elements of an
image cannot be directly accessed. Specific built-in <citerefentry href="imageFunctions"><refentrytitle>image read and write functions</refentrytitle></citerefentry> are provided to read from
and write to any location in the image. Pointers to image2d_t or image3d_t are not allowed.
image2d_t or image3d_t data types cannot be declared in a struct. image2d_t and
image3d_t cannot be used to declare local variables or as the return type of a function.
An image2d_t or image3d_t argument to a function cannot be modified.</para>

<para>Samplers cannot be declared as arrays, pointers, or be used as the type for local variables
inside a function or as the return value of a function defined in a program. Samplers
cannot be passed as arguments to functions called by a <citerefentry href="functionQualifiers"><refentrytitle>__kernel</refentrytitle></citerefentry> function. A sampler
argument to a __kernel function cannot be modified.	</para>
		</listitem>
		
		<listitem>
		<para>Bit-fields are currently not supported.</para>
		</listitem>
		
		<listitem>
		<para>Variable length arrays and structures with flexible (or unsized) arrays are not supported.</para>
		</listitem>
		
		<listitem>
		<para>Variadic macros and functions are not supported.</para>
		</listitem>
		
		<listitem>
		<para>The C99 standard headers <code>assert.h</code>, <code>ctype.h</code>, <code>complex.h</code>, <code>errno.h</code>,
<code>fenv.h</code>, <code>float.h</code>, <code>inttypes.h</code>, <code>limits.h</code>, <code>locale.h</code>, <code>setjmp.h</code>,
<code>signal.h</code>, <code>stdarg.h</code>, <code>stdio.h</code>, <code>stdlib.h</code>, <code>string.h</code>, <code>tgmath.h</code>,
<code>time.h</code>, <code>wchar.h</code>, and <code>wctype.h</code> are not available and cannot be included by a program.</para>
		</listitem>
		
		<listitem>
		<para>The <code>extern</code>, <code>static</code>, <code>auto</code>, and <code>register</code> storage-class specifiers are not supported.</para>
		</listitem>
		
		<listitem>
		<para>Predefined identifiers are not supported.</para>
		</listitem>

		<listitem>
		<para>Recursion is not supported.</para>
		</listitem>

		<listitem>
		<para>The function using the <citerefentry href="functionQualifiers"><refentrytitle>__kernel</refentrytitle></citerefentry> qualifier can only have return type <type>void</type> in the source code.</para>
		</listitem>

		<listitem>
		<para>Arguments to <citerefentry href="functionQualifiers"><refentrytitle>__kernel</refentrytitle></citerefentry> functions in a program cannot be declared with the built-in scalar types <type>bool</type>, <type>half</type>, <type>size_t</type>, <type>ptrdiff_t</type>, <type>intptr_t</type>, and <type>uintptr_t</type>. The size in bytes of these types except <type>half</type> are implementation-defined and in addition can also be different for the OpenCL device and the host processor making it difficult to
allocate buffer objects to be passed as arguments to a kernel declared as pointer to these types. <type>half</type> is not supported as <type>half</type> can be used as a storage format only and is not a data type on which floating-point arithmetic can be performed.</para>
		</listitem>

		<listitem>
		<para>Whether or not irreducible control flow is illegal is implementation defined.</para>
		</listitem>
		
		<listitem>
		<para>Built-in types that are less than 32-bits in size i.e. <type>char</type>, <type>uchar</type>, <type>char2</type>, <type>uchar2</type>, <type>short</type>, <type>ushort</type>, and <type>half</type> have the following restriction:</para>

<para>Writes to a pointer (or arrays) of type <type>char</type>, <type>uchar</type>, <type>char2</type>, <type>uchar2</type>, <type>short</type>, <type>ushort</type>, and <type>half</type> or to elements of a struct that are of type <type>char</type>, <type>uchar</type>, <type>char2</type>, <type>uchar2</type>, <type>short</type>, and <type>ushort</type> are not supported. </para>

<para>The kernel example below shows what memory operations are not supported on built-in types less than 32-bits in size.</para>
<literallayout><code>
          kernel void
          do_proc (__global char *pA, short b,
                         __global short *pB)
          {
                char            x[100];
                __private char  *px = x;
                int             id = (int)get_global_id(0);
                short           f;
                f = pB[id] + b; // is allowed
                px[1] = pA[1];  // error. px cannot be written.
                pB[id] = b;   // error. pB cannot be written
          }</code></literallayout>
		</listitem>

		<listitem>
		<para>Arguments to <citerefentry href="functionQualifiers"><refentrytitle>__kernel</refentrytitle></citerefentry> functions in a program cannot be declared to be of type <citerefentry href="otherDataTypes"><refentrytitle>event_t</refentrytitle></citerefentry>.</para>
		</listitem>
		
		<listitem>
		<para>Elements of a struct or union must belong to the same address space. Declaring a struct or union whose elements are in different address spaces is illegal.</para>
		</listitem>

		
		</itemizedlist>
    </refsect1>
	


<!-- ================================ SPECIFICATION  -->		
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    <refsect1 id="specification"><title>Specification</title>
        <para><imageobject><imagedata fileref="pdficon_small1.gif" format="gif" /></imageobject>
            <olink uri="restrictions">OpenCL Specification</olink>
        </para>
    </refsect1>  	

<!-- ================================ ALSO SEE  -->	
    <refsect1 id="seealso"><title>Also see</title>
        <para>
            <citerefentry href="imageFunctions"><refentrytitle>Image Functions</refentrytitle></citerefentry>, 
			<citerefentry href="functionQualifiers"><refentrytitle>Function Qualifiers</refentrytitle></citerefentry>
        </para>
    </refsect1>


<!-- ============================== COPYRIGHT -->
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    <refsect3 id="Copyright"><title></title>
			Copyright &#169; 
    </refsect3>

</refentry>